The present invention relates to a plasma display apparatus. More particularly, the present invention proposes a three-electrode AC (alternate current) type surface discharge plasma display apparatus with a new structure.
The plasma display apparatus (PDP apparatus) has been put to practical use as a flat display and is highly regarded as a thin high-luminance display. Among several types of the PDP apparatus, an AC type PDP, in which the light emission display is performed by applying a voltage waveform alternately to two sustain electrodes to keep on causing a discharge to occur, is mostly used. A discharge is completed 1μ second to a few μ seconds after the application of a pulse. Ions, which are positive charges generated by a discharge, accumulate on the surface of the insulating layer on an electrode to which a negative voltage is being applied, and electrons, which are negative charges, accumulate on the surface of the insulating layer on an electrode to which a positive voltage is being applied.
Therefore, after wall charges are first formed on a cell to be displayed by selectively causing a discharge to occur with a pulse (write pulse) of a high voltage (write voltage), if a pulse (sustain pulse or sustain discharge pulse) of a voltage lower (sustain voltage or sustain discharge voltage) than before and of the opposite polarity is applied, a threshold value of discharge voltage is exceeded and a discharge is caused to occur in the cell to be displayed because the voltage due to the wall charges accumulated thereon is overlapped and a large voltage develops across the discharge space. (A discharge is not caused to occur in a cell not to be displayed, to which a write pulse has not been applied, even if a sustain pulse is applied.) In other words, a cell, in which wall charges have been formed once by a write discharge, has a characteristic that a discharge is kept on by continuing to apply a sustain pulse, the polarity of which being alternately reversed. This is called the memory effect. Generally, an AC type PDP apparatus performs a display by utilizing this memory effect.
The AC type PDP apparatuses include the two-electrode type, in which a selection discharge (address discharge) and a sustain discharge are caused to occur by two electrodes, and the three-electrode type, in which an address discharge is caused to occur by utilizing a third electrode. The color PDP apparatus that performs a gray level display excites the phosphor formed in a discharge cell by the ultraviolet rays generated by a discharge, but the phosphor has a drawback of being susceptible to the impact of ions, which are positive charges generated by the discharge. Because the above-mentioned two-electrode type has a structure in which the phosphor is directly hit by ions, the life of the phosphor may be shortened. To avoid this, a color PDP apparatus generally employs the three-electrode structure that utilizes the surface discharge. The three-electrode type further includes two types: in one type a third electrode is formed on the same substrate on which a first and a second electrodes that perform the sustain discharge have been arranged, and in the other type the third electrode is arranged on another opposing substrate. On the other hand, when the three kinds of electrodes are formed on the same substrate, there are two types: in one type the third electrode is arranged over the two electrodes that perform the sustain discharge, and in the other type the third electrode is arranged thereunder. Still furthermore, there are two types: in one type the visible light emitted from the phosphor is viewed therethrough (transparent type), and in the other type that reflected by the phosphor is viewed (reflection type).
FIG. 1 is a rough plan view of the panel to be used in the above-mentioned three-electrode surface discharge AC type PDP apparatus. FIG. 2 is a rough sectional view in the vertical direction of a discharge cell of the panel in FIG. 1 and FIG. 3 is that in the horizontal direction that shows an example of the reflection type in which part of the sustain electrode is formed by a transparent electrode on the panel on which the third electrode (address electrode) is formed on another substrate different from and opposing the substrate having the electrodes that perform the sustain discharge.
As shown in FIG. 1, plural first electrodes (X electrodes) 12 and second electrodes (Y electrodes) 11-1 to 11-N are arranged adjacently by turns and plural third electrodes (address electrodes) 13-1 to 13-M are arranged in the direction perpendicular thereto. A partition wall 14 is formed between address electrodes. The X electrodes 12 are connected commonly. A display cell is formed at the crossing of each pair of the X electrode 12 and the Y electrode 11 and each address electrode 13. Therefore, each display cell is separated in the horizontal direction by the partition wall 14 but is continuous with the display cells contiguous thereto in the perpendicular direction. Therefore, the gap between the pairs of the X electrode 12 and the Y electrode 11 is vertically widened to prevent adjacent display cells from affecting each other.
The panel is composed of two glass substrates 21 and 29. On the first substrate 21, the plural first electrodes (X electrodes) 12 and the plural second electrodes (Y electrodes) 11, which correspond to the sustain electrodes and are arranged adjacently by turns, are formed and these electrodes are composed of transparent electrodes 22a and 22b and bus electrodes 23a and 23b. Because of the role to allow the light reflected by the phosphor to pass through, the transparent electrode is made of such as ITO (transparent film the main component of which is indium oxide). The bus electrode needs to be made of a material of a low resistance therefore is made of Cr (chromium) or Cu (copper), because it is necessary to avoid the reduction in voltage due to the electrical resistance. Moreover, the bus electrode is covered with a dielectric layer (glass) 24 and an MgO (magnesium oxide) film 25 is formed as a protection film on the discharge surface. On the other hand, on the second substrate 29 that opposes the first glass substrate 21, the plural third electrodes (address electrodes) 13 are formed in the direction perpendicular to that of the sustain electrodes (X, Y electrodes). The partition wall 14 is formed between the address electrodes and between the partition walls, phosphors 27 that have the light emission characteristics of red (R), green (G), and blue (B) are formed so as to cover the address electrode. The two glass substrates are assembled so that the ridge of the partition wall 14 and the MgO film 25 come into close contact with each other. The space between the phosphor 27 and the MgO film 25 is a discharge space 26.
The method to drive the above-mentioned three-electrode surface discharge AC type PDP apparatus is called the “Address/sustain discharge period separated type-write address method”. This drive method is briefly described below. In the first reset period, each display cell is set to a uniform state. In this reset period, all the display cells are set to a uniform state by applying a voltage sufficiently greater than the threshold voltage between the X electrode and the Y electrode to cause a discharge to occur, while a fixed voltage (0V, for example) is being applied to the address electrode, then neutralizing the charges generated by the discharge by making the potentials of the X electrode and the Y electrode equal to each other. In the next address discharge period, with a state in which a fixed voltage is being applied to the X electrode, a scan pulse of, for example, −150 V is applied sequentially to the Y electrode, a write pulse (of 50 V, for example) is applied to the address electrode of a cell to be made to emit light in synchronization with the application of each scan pulse, and no write pulse is applied (that is, 0 V is applied) to the address electrode of a cell not to be made to emit light. In this way, a discharge is caused to occur in a cell to be made to emit light and wall charges are formed on the surface of the dielectric on the X electrode and the Y electrode, but no wall charge is formed in a cell not to be made to emit light. In the next sustain discharge period, with a state in which a fixed voltage (0 V, for example) is being applied to the address electrode, a sustain pulse is applied alternately to the X electrode and every Y electrode. The sustain pulse has such a voltage (180 V, for example) that a sustain discharge is caused to occur in a cell to be made to emit light, in which the wall charges have been formed during the address discharge period, by overlapping the voltage due to the wall charges because the threshold voltage is exceeded, but no discharge is caused to occur in a cell not to be made to emit light in which no wall charge has been formed. As the occurrence of a sustain discharge forms the wall charges of the opposite polarity, a discharged is caused to occur if a sustain pulse of the opposite polarity is applied subsequently. In this way, a discharge is kept on, due to the memory effect, by applying a sustain pulse the opposite polarity of which is alternately changed. What contributes to the display is this sustain discharge and, the longer the sustain discharge period, the higher the light emission luminance is. By repeating the above-mentioned reset period, address discharge period, and sustain discharge period, the display is performed.
In the PDP apparatus, it is possible only to control the display cell whether to emit light or not, but the light emission intensity cannot be changed for each display cell. Therefore, when the gray level display is performed, one display frame is made to comprise plural subframes. Each subframe is composed of a reset period, an address discharge period, and a sustain discharge period, and the light emission intensity is varied by changing the length of the sustain discharge period. Then, a desired light emission luminance can be obtained by selecting the subframes to be made to emit light in one display frame for each display cell.
The PDP apparatus comprises a drive circuit to apply a voltage to each electrode of the panel described above, a frame memory to convert display data into a signal appropriate for the drive signal in the PDP apparatus, control circuits of each part, and so on, and, as these are widely known, a description is omitted here. Although various examples of modification to such as the panel structure and the drive method have been proposed, no description about these is provided here.
For the three-electrode surface discharge AC type PDP apparatus that has been known so far, various figures of the electrode to improve the discharge efficiency have been proposed, but it can be said, on the whole, that the X electrode and the Y electrode, which are the sustain electrodes, are designed so as to extend in the same direction.
For a gas discharge display apparatus such as the PDP apparatus that performs the image display, it is required to prevent a discharge in a display cell from affecting adjacent display cells to cause a discharge to occur in a cell not to be made to emit light, and to keep on causing a discharge to occur in a cell to be made to emit light, therefore, a structure in which display cells are separated is needed. In the above-mentioned three-electrode surface discharge AC type PDP apparatus, for example, the gap between the pairs of the x electrode 12 and the Y electrode 11 is vertically widened to prevent adjacent display cells from affecting each other and the wall partition 14 is provided to horizontally separate the display cells, as described above. Such a structure, however, has the following problems. One of them is that although the wall partition is separated horizontally, if there exists a flaw in the wall partition, a charge may flow to an adjacent cell, not to be made to emit light, through it, a discharge may be caused to occur in the cell not to be made to emit light by the charge as a trigger, and an erroneous display may be caused. Another problem is that the gap between the pairs of the X electrode 12 and the Y electrode 13 is vertically widened to prevent a discharge from being caused to occur, therefore, the vertical interval between the display cells needs to be also widened, and as a result the density of display cells cannot be increased.
Moreover, the panel structure of the above-mentioned three-electrode surface discharge AC type PDP apparatus has still another problem that since the sustain electrodes (X electrodes and the Y electrodes) are arranged in parallel, the panel volume becomes large and it is necessary to use a drive circuit of a higher performance accordingly, resulting in a larger power consumption and a higher cost.